The present invention is described largely in connection with an exemplary usage in touch panels. It will be appreciated that principles of this invention are applicable to other fields employing electrode arrays, being more broadly applicable to networks of switchable sensing and/or driving electrodes, such as for example display devices generally, sensors, and radio frequency (RF) antennae arrays as mentioned above. Given the significant application to touch panels as a principal example, background technology pertaining to touch panels is described in this section, with the principles of the invention being expandable to other electrode array fields.
Touch panels have become widely adopted as the input device for a range of electronic products such as smart-phones, tablet devices, and computers. Most high-end portable and handheld electronic devices now include touch panels. These are most often used as part of a touchscreen, i.e., a display and a touch panel that are aligned so that the touch zones of the touch panel correspond with display zones of the display.
The most common user interface for electronic devices with touchscreens is an image on the display, the image having points that appear interactive. For example, the device may display a picture of a button, and the user can then interact with the device by touching, pressing or swiping the button with a finger or with a stylus. For example, the user can “press” the button and the touch panel detects the touch (or touches). In response to the detected touch or touches, the electronic device carries out some appropriate function. For example, the electronic device may turn itself off, execute an application, perform some manipulation operation, and the like.
Although, a number of different technologies can be used to create touch panels, capacitive systems have proven to be the most popular due to their accuracy, durability, and ability to detect touch input events with little or no activation force. A basic method of capacitive sensing for touch panels is the surface capacitive method—also known as self-capacitance—for example as disclosed in U.S. Pat. No. 4,293,734 (Pepper, issued Oct. 6, 1981). A conventional implementation of a surface capacitance type touch panel is illustrated in FIG. 1, which includes a transparent substrate 10, the surface of which is coated with a conductive material that forms a sensing electrode 11. One or more voltage sources 12 are connected to the sensing electrode, for example at each corner, and are used to generate an electrostatic field above the substrate. When an input object 13 that is electrically conductive—such as a human finger—comes into close proximity to the sensing electrode, a capacitor 14 is dynamically formed between the sensing electrode 11 and the input object 13 and this field is disturbed. The capacitor 14 causes a change in the amount of current drawn from the voltage sources 12 wherein the magnitude of current change is related to the distance between the finger location and the point at which the voltage source is connected to the sensing electrode. Current sensors 15 are provided to measure the current drawn from each voltage source 12, and the location of the touch input event is calculated by comparing the magnitude of the current measured at each source. Although simple in construction and operation, surface capacitive type touch panels are unable to detect multiple simultaneous touch input events as occurs when, for example, two or more fingers are in contact with the touch panel.
Another well-known method of capacitive sensing applied to touch panels is the projected capacitive method—also known as mutual capacitance. In this method, as shown in FIG. 2, a drive electrode 20 and sense electrode 21 are formed on a transparent substrate (not shown). A changing voltage or excitation signal is applied to the drive electrode 20 from a voltage source 22. A signal is then generated on the adjacent sense electrode 21 by capacitive coupling via the mutual coupling capacitor 23 formed between the drive electrode 20 and sense electrode 21. A current measurement device 24 is connected to the sense electrode 21 and provides a measurement of the size of the mutual coupling capacitor 23. When the input object 13 is brought to close proximity to both electrodes, it forms a first dynamic capacitor to the drive electrode 27 and a second dynamic capacitor to the sense electrode 28. If the input object is connected to ground, as is the case for example of a human finger connected to a human body, the effect of these dynamically formed capacitances is manifested as a reduction of the amount of capacitive coupling in between the drive and sense electrodes, and hence a reduction in the magnitude of the signal measured by the current measurement device 24 attached to the sense electrode 21.
As described, for example, in U.S. Pat. No. 5,841,078 (Bisset et al, issued Oct. 30, 1996), by arranging a plurality of drive and sense electrodes in a grid pattern to form an electrode array, this projected capacitance sensing method may be used to form a touch panel device. An advantage of the projected capacitance sensing method over the surface capacitance method is that multiple simultaneous touch input events may be detected.
Devices have been disclosed in which the touch panel can switch between self-capacitive and projected or mutual capacitive modes by means of switches. For example, US 2014/0078096 (Tan et al., published Mar. 20, 2014) applies a method to fixed touch panel patterns. The objective of this capability is to use either mode when it is more beneficial for object detection. Moreover, some devices allow the change of shape or size of the sense and drive electrodes, or their spatial arrangements. For example, U.S. Pat. No. 8,054,300 (Berstein, issued Nov. 8, 2011) proposes a method of reconfigurability by means of switches located on the side of the panel or in a separate board.
In many touchscreens the touch panel is a device independent of the display. The touch panel sits on top of the display, and the light generated by the display crosses the touch panel, with an amount of light being absorbed by the touch panel. In more recent implementations, for example U.S. Pat. No. 7,859,521 (Hotelling et al., issued Dec. 28, 2010), part of the touch panel is integrated within the display stack, and the touch panel and display may share the use of certain structures, such as transparent electrodes. This integration of the touch panel into the display structure seeks to reduce price by simplifying manufacture, as well as reducing the loss of light throughput that occurs when the touch panel is independent of the display and located on top of the display stack.
Another fully integrated touch panel is described in U.S. Pat. No. 8,390,582 (Hotelling et al., issued Mar. 5, 2013). The disclosed device uses additional signal lines and transistors to switch between display functionality and self-capacitance touch panel functionality, requiring at least three additional transistors per pixel. Display RGB data lines are connected to source/drain transistor terminals, and act as either voltage drive lines or charge sense lines, which prevents the concurrent driving of touch panel and display.
An enhanced integrated active matrix touch panel is disclosed in Applicant's commonly owned PCT publication number WO 2017/056500 (Gallardo et al., published Apr. 6, 2017), which is incorporated here by reference. As an integrated touch panel, the device is operable in either one of a self-capacitance touch sensing mode or a mutual capacitance touch sensing mode. The device includes both a display and a touch panel, and so is operable both as display and as a touch panel (although not necessarily simultaneously). The device is integrated in the sense that at least some components are common to both the touch panel and the display.
As described in WO 2017/056500, an active matrix touch panel (AMTP) is an in-cell technology by which all the components of the touch panel are integrated into the same substrate as the display circuitry, with which the touch panel shares space. In-cell or integrated touch panels save cost to the display manufacturer. In-cell touch panels, however, pose new problems, as normally the available space is very limited. Frequently, some components have to be shared between the display and touch panel components. For AMTP, the touch panel and the displays share the top electrode, also referred to as the common electrode or VCOM.
FIG. 3 is a drawing depicting an overview of an exemplary pixel arrangement 30 in a typical display system. The pixel arrangement 30 may include individual pixels 32 that are grouped into touch panel (TP) elements 34 that permit the touch panel operations described above. In a typical display, each pixel has a top electrode, and the pixel top electrodes combine into a single, continuous top electrode corresponding to VCOM as referenced above. For AMTP, the VCOM is patterned into a two-dimension array of touch panel elements 34. Each touch panel element covers a number of pixels, and the top electrode of these pixels is a component of the respective touch panel element. In this manner, therefore, the display and touch panel share the VCOM electrode.
FIG. 4 is a drawing depicting an exemplary AMTP structure comparably as taught in WO 2017/056500. In such configuration, a basic unit cell 36 includes a plurality of the individual pixels 32 arranged in an array. In this example, a basic unit cell 36 includes a 3×2 pixel array. The touch panel element 34 in turn includes an array of unit cells 36 arranged in parallel. A typical example may incorporate 100 unit cells 36 within a touch panel element 34, resulting in 600 individual pixels per touch panel element.
FIG. 5 is a drawing depicting an exemplary array 38 of touch panel elements 34, as may be incorporated into a touch panel display system. An exemplary electrical interconnection of the touch panel elements is shown in this figure. Each touch panel element can be connected either to a sense line (SEN) or to a function line (FNC). These connections are made by two thin film transistors (TFTs), denoted M1 and M2. Gate select lines SEL and SELB are operable to switch M1 versus M2 open or closed, thereby controlling whether the touch panel is electrically connected to SEN (via operation of the SEL gate line) or to FNC (via operation of the SELB gate line). The SEN lines connect to the sensing circuitry of a touch panel controller (TPC), so that touch signals can be read and measured. The FNC lines can either supply a driving signal from a display driver, or can be connected to ground for performing different functions of the pixels.
FIG. 6 is a drawing depicting an exemplary configuration of a unit cell 36, including electrical interconnections comparably as depicted in FIG. 5. The unit cell 36 employs the 3×2 pixel configuration referenced above, with FIG. 6 further illustrating the color sub-pixels red, blue, and green for each individual pixel 32 along with the respective interconnection lines. RGB TFTs are connected to a display gate line for control of light emission from the various sub-pixels via the RGB TFTs associate with the color sub-pixels. The M1 and M2 TFTs for this unit cell also are shown, as connected to the select, sense, and function lines as referenced above with respect to FIG. 5. The available space for touch panel TFTs and connection lines is very limited, because most of the display area needs to be dedicated to the optical aperture for letting light through from the light source at the non-viewing side of the display system. The available space is fragmented, and typically is configured of small spaces at the side of the RGB TFTs. A single TFT potentially could be used to switch each pixel, but such a configuration would be too resistive for a touch panel element. Accordingly, to form the touch panel element multiple unit cells are connected in parallel, with, as referenced above, the basic AMTP unit cell including six pixels arranged in an array of three rows by two columns. The basic unit cell configuration can be modified, for example to include additional TFTs for added functionalities. WO 2017/056500 describes several embodiments with modified unit cells, allowing different drive and sense schemes.
A deficiency of conventional systems that employ arrays of electrodes, such as for example conventional touch panels, is that the control signal connections such as driving or sensing are selectable generally upon only a row or a column basis. Individual electrode elements generally are not individually selectable for control, and thus there are limitations on electrode control patterns which in turn may limit usage of conventional systems.